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Provides common utility functions

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/*
 * Copyright (c) CQSE GmbH
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.conqat.lib.commons.collections;

/**
 * Comparator that compares objects based on the identifiers provided by a {@link IIdProvider}.
 * 
 * @author deissenb
 */
public class IdComparator, T> extends IdentifierBasedComparatorBase {

	/** ID provider used for comparing. */
	private final IIdProvider idProvider;

	/** Create new comparator. */
	public IdComparator(IIdProvider idProvider) {
		this.idProvider = idProvider;
	}

	/**
	 * Obtain identifier from identifier provider.
	 * 
	 * @throws NullPointerException
	 *             if the id provider returns null.
	 */
	@Override
	protected I obtainIdentifier(T t) {
		I id = idProvider.obtainId(t);
		if (id == null) {
			throw new NullPointerException("Id for " + t + " is null.");
		}
		return id;
	}
}